Incandescent lamp having a ceramic screw type base



March 10, 1970 A. E. WESTLUND, JR,, ETAL. 3,500,105

INCANDESCENI' LAMP HAVING A CERAMIC SCREW TYPE BASE Filed Feb. 19, 1968 INVENTORS ROBERT M. GRIFFIN ARNOLD E. WESTLUND JR.

M BY ATTORNEY United States Patent O U.S. Cl. 313-318 Claims ABSTRACT OF THE DISCLOSURE A screw base arrangement for a lamp having a pressseal at one end. The arrangement includes an enlarged cylindrical ceramic holder having a small screw shell centered on an extension projecting from the base portion of the holder. The holder is provided with a pair of vertical intersecting relief slots extending short of the full length of the holder. One slot is narrower in width and utilized to hold the lamp while the other intersecting slot provides a relief area junctured at the seal of the lamp. This relief area allows heat generated in the seal area to be dissipated by air currents.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to high current lamps having tungsten filaments enclosed in sealed envelopes, the latter being of fused quartz or other suitable glass. Such devices generally contain a halogen, such as iodine or bromine, and are usually called halogen-quartz lamps. They operate on a regenerative cycle, initiated when a tungsten halide is produced and chemically combines with the particles evaporated from the incandescing tungsten filament. Subsequent thermal decomposition of this compound replaces the tungsten particles on the filament. More particularly, this invention concerns an improved base arrangement for lamps having a press-seal at one end. Specifically, high wattage lamps that require attachment to existing miniature sockets arrayed in fixtures where confinement generates heat build-up.

Description of the prior art Briefly, in the fabrication of quartz-halogen lamps the important sealing operation includes using wafer-thin strips of molybdenum as current conductors in the seal area. These strips are welded between a lead-in wire and a filament-support wire and assembled into a quartz tubular envelope, thereafter a softening of the quartz and a mechanical sealing die is utilized to form the seal. This sealing operation pinches the area where the molybdenum strip bridges the lead-in wires and provides a vacuumtight seal.

The problem encountered with the use of molybdenum foil as a seal conductor in high wattage lamps are many. But the most critical is that when current is passed through the foil, a continuous heat build-up occurs because of the low thermal conductivity of the quartz.

Normally in the basing of high wattage lamps where a screw base is needed, a ceramic base holder is utilized as an intermediate between the lamp and screw shell. In the forming of a lamp holder of this description, a conventional, formable ceramic material is used. The basic shape comprised a slot for receiving a press-sealed, single-ended lamp and a protrusion for supporting a screw shell. The holder is fabricated by compressing the ceramic material to the basic shape; thereafter it is fired for hardening. The metal screw shell is then attached to the holder. In this particular application the holder is formed to have a re- 3,500,105 Patented Mar. 10, 1970 duced circular ceramic extension at its base for the attachment of a miniature screw shell.

The lamp is then fitted and aligned into the formal slot of the ceramic holder and secured therein by applying a basing cement completely around the flat press-seal of the lamp. This completed lamp assembly, where basing cement is used to completely cover the seal area, produces a lamp assembly of a limited range of operating temperatures.

The cement having poor thermal conductive properties acts as an insulator and contains the heat generated in the molybdenum seals. When heat builds up to the vicinity of 350 C., a break-down of the molybdenum seals occurs causing early lamp failure.

SUMMARY OF THE INVENTION According to our invention we have overcome this decided disadvantage by redesigning the ceramic holder to provide for cooler operation, particularly in the press-seal area of the lamp.

The holder of our invention is formed with two intersecting slots. One slot is cut through the holder while the other slot is of a shorter length, whereby the ends are enclosed by the outer walls of the holder. When the pressseal portion of the lamp is opsitioned in the shorter of the two slots, the other slot provides a clear path on both sides of the seal area. The lamp is then aligned and cement is applied only on the enclosed side portions of the pressseal. This leaves the flat portion of the seal free of cement. With this arrangement, the molybdenum ribbon press-seal area is exposed thereby dissipating heat generated by the wafer foils.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a view of the lamp and base in a pre-assembled position.

FIG. 2 is a perspective view of a completed based lamp.

FIG. 3 is a cross-sectional view of the base taken on the line 33 of FIG. 2.

FIG. 4 is an elevational view of the completed lamp assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, the lamp and socket arrangement of our invention comprises a hermetically sealed vitreous envelope 10 which contains a coiled-coil tungsten filament 12 connected at its ends to respective lead-in conductors comprising inner and outer portions 14 and 16 respectively. The inner and outer, lead-in wires are separated in the seal area by molybdenum foil strips 18 which are hermetically sealed in spaced-apart relation in a compressed protruding seal portion 20, formed at one end of the envelope. The outer portions 16 of the lead-in conductors extend beyond this press-seal area 20.

The particular lamp shown is of well-known iodinecycle type whre during lamp operation a small amount of iodine vapor functions as a getter to combine with tungsten that is vaporized from the filament 12 onto the envelope wall to thereby form a tungsten iodide which migrates back to the vicinity of the filament, where it then redeposits tungsten onto the filament and releases iodine for continuation of the cycle.

As viewed in FIG. 1, the lamp and base are illustrated in a preassembled relationship. The main elements are the lamp 10 and a preformed ceramic lamp holder 24 joined of conventional material. In the forming of the lamp holder 24, a pair of intersecting slots 26 and 28 are vertically formed terminating short of the base 30. Slot 28 is cut completely through the base 24 while the other slot 26 terminates short of the sides of the holder 24 defining the confined end areas. Protruding from the base portion 30 of the holder is a hollow lug 36 extending below the surface of the base 30. This lug is utilized for the attachment of a conventional screw shell 38. A contact bead 401ocated at the outer end of the lug is separated from the shell 38 by a conical insulating spacer 42.

In positioning the lamp into the holder 24, the flat press-seal portion is placed within the slot 26. As viewed in. FIG. 3, which is a cross-sectional view of the holder, the press-seal portion of the lamp is smaller than the dimensions of the slot 26. The space at either end of the enclosed part of the slot are then filled with a suitable basing cement. It can be mentioned at this time that prior to cementing the lamp to the holder, more specifically when the lamp is slid into the slot 26, the lead-in wires 16 are fed through a slot in the base of the holder, not shown in the drawing. One of the wires is passed through a slot in the lug 36 and then attached to the top part of the screw shell 38. The other lead-in wire is directed through the hollow hub to the contact bead 40. A conventional welding operation secures the wires to their respective points of contact. Also prior to the final setting of the cement the lamp and holder are optically aligned to-provide the required lamp operational efficiency.

In FIGS. 2 and 3 the lamp 10 is shown in register with the holder 24. It can clearly be seen that the length of the press-seal portion 20 of the lamp is shorter than the depth of the slot 26. This provides a clearance 46 between the bottom of the press-seal and the bottom of the slots. During operation of the lamp the excessive heat radiated in the foil section 18 is carried away by air currents passing over and under the seal area.

It is apparent that other changes and modifications may be made within the scope of the instant invention but it is our intent, however, to be limited only by the scope of the appended claims.

What We claim is:

1. An electrical device comprising:

a sealed envelope of vitreous material having a pressseal at one end thereof;

a pair of lead-in wires hermetically sealed by way of molybdenum foil through said press-seal in spaced apart relationship to one another and extending beyond said press-seal;

said lead-in wires being connected at their inner ends to a filament;

a ceramic holder provided with two vertical intersecting slots extending short of the length of said holder;

the first of said slots being cut through said holder while the second of said slots has its ends confined within said holder;

said lamp being positoned within said second slot whereby said edges of said press-seal are in register with said closed ends of said second slot and said first slot provides an air access to both sides of said press-seal;

a screw base attachment centrally located and extending beyond the base of said holder and said lead-in wires being in electrical connection therewith;

means for rigidly holding said lamp in optical alignment in said holder.

2. The electrical device according to claim 1 wherein one of said intersecting slots penetrates the outer Walls of said holder.

3. The electrical device according to claim 1 wherein said press-seal of said lamp is shorter than the depth of said slots, thereby leaving an air space between the bottom of said seal and the inside of said holder for the circulation of air.

4. The electrical device according to claim 1 wherein means for holding said lamp is basing cement applied to the closed ends of said second slot.

5. The electrical device according to claim 1 wherein said molybdenum foil sections are exposed by said first slot.

References Cited UNITED STATES PATENTS 3,327,283 6/1967 Anderson et al. 3133l8 X 3,413,511 11/1968 Plagge 3l3-318 3,417,367 12/1968 Dayton et al. 3133l8 X 3,431,540 3/196'9 Kopelman et al. 3133l8 X FOREIGN PATENTS 284,693 6/1928 Great Britain. 299,411 8/ 1965 Netherlands.

JOHN W. HUCKERT, Primary Examiner A. J. JAMES, Assistant Examiner US. Cl. X.R. 313274, 315 

